1. Field of the Invention
The invention relates to a process for the thermal treatment of carbon-containing substances, in particular, of sludges which after mechanical indirect predrying, are subjected to direct drying by means of drying gas.
2. Description of the Prior Art
The journal "cay" (chemie-anlagen+verfahren), May 1984, pages 50 and 146, discloses a procedure wherein mechanically pre-dehydrated sewage sludge is dried in a fluidized bed before being burned. The particular disadvantage of this procedure is that the dried sludge is burned in a single stage. Thus, noxious substances, e.g., SO.sub.2, NO.sub.x, dust, and heavy metals, are present, in relatively large amounts, in the flue gas from which they have to be separated. The entire amount of ashes produced is also entrained with the flue gas stream. A further disadvantage of the known procedure is the formation of odorous substances during drying of the sewage sludge by the hot flue gases. These substances have to be subjected to an energy consuming post-combustion or to an expensive gas purification.